Method for Recycling Streams in a Separations Process

ABSTRACT

A method and apparatus for recycling streams in a separations process comprising: determining a measured reading of a parameter of the separations processor is in a suboptimal range; separating, via a separation unit having a volume of contact fluid, the inert gas from the pollutant gas in the inlet flue gas stream to form a clean gas stream and a purified pollutant gas stream; removing at least 1% of the volume of contact fluid to form a removed volume of contact liquid; performing some unit operations on the removed volume of contact fluid; injecting the clean gas stream into the inlet flue gas stream to form a flue gas stream of lower pollutant concentration; and, repeating at progressively lower pollutant concentration, as the inlet stream until the processor determines that a measured reading of the parameter has been returned to a substantially optimal range.

TECHNICAL FIELD

The disclosure relates to separations equipment for sequestering pollutants.

BACKGROUND

Greenhouse gas emissions are among the highest forms of pollution, and are closely monitored. Carbon dioxide (CO2) is the highest source of these greenhouse gas emissions, accounting for 80.9% of all greenhouse gas emissions in the U.S. in 2014, according to the EPA. Efforts are being made to reduce the amount of CO2 emissions. One method is that of carbon capture or sequestration. This is used mainly in industrial processes and power plants, to remove the CO2 before the flue gases are released to the atmosphere.

Flue gas is a product of combustion of wood, coal, natural gas, or other fossil fuels, and is released through a smokestack. Thus, it has a high CO2 concentration. There are many methods in development and in use to decrease the CO2 content of flue gas. It is important to verify that these methods are effective.

In monitoring and regulating CO2 emissions, simulations are often used. For example, the National Institute of Metrology created a Smoke Stack Simulator (SMSS) to study accurate measurement methods for flue gas flow rates. The SMSS was created to model many systems, with the capability to simulate flow fields by generating different swirls. Similarly, the flue gas itself can be simulated. Flue gas is typically composed mainly of carbon dioxide, water vapor, nitrogen, and oxygen. There may also be a small percentage of fly ash or other pollutants. The majority of the flue gas is usually made up of nitrogen—typically, two-thirds or more.

BRIEF SUMMARY

Contacts and carrier fluids may be used, such as:

1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, or vinyl fluoride.

The present disclosure describes systems and methods for recycling separated gases to simulate flue gas. Gases that may be used include an inert gas selected from the list comprising nitrogen, oxygen, air, water, and combinations thereof. A pollutant gas may also be used, selected from the list comprising carbon dioxide, sulfur oxides, nitrogen oxides, fly ash, mercury, arsenic, other pollutants present in flue gas, and combinations thereof. The present disclosure will discuss using only carbon dioxide and nitrogen as an example, however other gases may be used as mentioned above. If other gases are used, there may be obvious variations to the process described in this disclosure. The given example is meant to demonstrate one application of the systems and methods, and is not meant to limit the scope of the invention. Flue gas may be simulated by mixing the desired gases—in this case, carbon dioxide and nitrogen—from a supply source. The concentration of carbon dioxide in this simulated flue gas stream may range from 3% to 30% carbon dioxide. The simulated flue gas stream may be monitored by a pressure transducer. The pressure transducer may allow control over a valve through which the supply nitrogen may be regulated, keeping the simulated flue gas stream at a set pressure. In some preferred embodiments, the set pressure may be constant and positive, and may range from 0.1 psig to 2 psig. In some other embodiments, such as using a compressed simulated flue gas, the set pressure may range from 50 psig to 100 psig. The valve may be a solenoid valve, an actuated ball valve, or a mass flow controller. The supply carbon dioxide may be injected and regulated through a mass flow controller (MFC 1).

The simulated flue gas stream may also be monitored by a flowmeter. The flowmeter may communicate with a blower for the simulated flue gas stream, allowing the blower to operate in such a way to maintain a constant set flow rate for the simulated flue gas stream. The set flow rate may be set by the operator and may be at least 5 SCFM. In some embodiments, the set flow rate may be between 5 SCFM and 100 SCFM.

There may be a first analyzer placed before the separation unit. This analyzer may monitor the conditions of the simulated flue gas stream, including the concentration of carbon dioxide in the simulated flue gas stream just before entering the separation unit.

The simulated flue gas stream may then enter the separation unit. The separation unit may employ any carbon dioxide (or other pollutant gas) separation process, and may be able to process the entire flow rate of the simulated flue gas stream. For example, in some preferred embodiments, the separation unit may be a Cryogenic Carbon Capture process capable of processing 5 to 100 SCFM of simulated flue gas, using carbon dioxide as the pollutant gas. The separation unit may remove the carbon dioxide from the simulated flue gas stream, forming two outlet streams: a clean gas stream and a purified carbon dioxide stream. The purified carbon dioxide may consist only of carbon dioxide from the simulated flue gas stream. The clean gas stream may consist of all other non-carbon dioxide gases from the simulated flue gas stream, as well as any carbon dioxide that was not removed by the separation unit. In some preferred embodiments, such as one using the Cryogenic Carbon Capture process, the carbon dioxide concentration in the clean gas stream may range from 0.10% to 3%.

Both streams exiting the separation unit may be recycled, but they may pass through other steps before recombining. The clean gas stream may pass through a second analyzer, placed after the separation unit. This analyzer may monitor the concentration of carbon dioxide in the clean gas stream. When compared to the carbon dioxide concentration data from the first analyzer, which is placed in the simulated flue gas stream, the performance of the separation unit may be monitored.

The purified carbon dioxide stream may pass through a mass flow controller (MFC 2). MFC 2 may monitor the flow rate of the purified carbon dioxide stream. This flow rate data may enable feed-forward control on another mass flow controller (MFC 3 (110)) through which excess carbon dioxide may be released. This excess carbon dioxide may be vented, compressed and stored, or returned to the supply from which it came. Similarly, in some embodiments, the excess nitrogen may be vented or stored via a fourth mass flow controller (MFC 4).

In some preferred embodiments, the purified carbon dioxide stream may exit the separation unit at a high pressure. This pressure may be in the range of 70 psig to 150 psig. The pressure of the purified carbon dioxide stream may need to be decreased before continuing in the process, especially if the clean gas stream is at a lower pressure. A pressure regulator may be implemented for this purpose. The purified carbon dioxide stream, after passing through the pressure regulator, may be lowered to a pressure in the range of 30 psig to 50 psig. In some embodiments, the purified carbon dioxide stream may be a liquid, and may need to be vaporized using a heater or a warm process stream before continuing in the process. In these embodiments wherein the purified carbon dioxide stream is a liquid, the excess carbon dioxide flowing through MFC 3 may remain a liquid and be pumped into a bottle.

The purified carbon dioxide stream and the clean gas stream may then combine. The point at which the purified carbon dioxide is injected may be important. It may be located at a point sufficiently downstream of the second analyzer that the recycled and carbon dioxide is not picked up by the second analyzer, and sufficiently upstream of the first analyzer that the gas is well mixed in the simulated flue gas stream before passing through the first analyzer. The carbon dioxide supply may also be injected at this same combination point through MFC 1. The first analyzer may also provide data that allows the controller to regulate each of the mass flow controllers. MFC 1 and MFC 3 may be controlled such that the concentration of carbon dioxide in the simulated flue gas stream is kept at a set value, as measured by the first analyzer.

The combined clean gas, purified carbon dioxide, and supply carbon dioxide form the recycle stream. The supply nitrogen may later injected into this recycle stream through the valve. This valve may be regulated using data from the pressure transducer to maintain the set pressure mentioned above. After the point of nitrogen injection, the simulated flue gas may be reformed and again flows into the separation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the invention briefly described above is made below by reference to specific example. Several examples are depicted in drawings included with this application. An example is presented to illustrate, but not restrict, the invention.

FIG. 1 is a schematic diagram of an experimental system which simulates and separates flue gas in a regulated and monitored environment.

FIG. 2A is an illustration of the system of FIG. 1.

FIG. 2A is an illustration of the piping and instrumentation shortly before and after the separation unit.

FIG. 3 is a schematic diagram of a system which simulates, separates, and recycles flue gas, including a device to lower the pressure of the purified carbon dioxide stream.

FIG. 4 is a schematic diagram of a system which simulates flue gas, separates it into a carbon dioxide component and a clean gas component, and recycles the components.

FIG. 5 is a schematic diagram of the system in FIG. 1, in the embodiment that the purified carbon dioxide stream is a liquid, only displaying the section of the system after the separation unit.

FIG. 6 is a method diagram of the system in FIG. 1.

DETAILED DESCRIPTION

The systems and methods disclosed herein relate to simulating flue gas and separating gases in the flue gas stream, then recycling the gases to again simulate the flue gas. These methods may be used to test the effectiveness of a separation unit. For example, carbon dioxide and nitrogen may be combined at a desired concentration to simulate a flue gas. This simulated flue gas may be regulated and analyzed, and then sent through a separation unit. The separated streams which may be formed—one of clean gas comprised mostly of nitrogen and one of purified carbon dioxide—may also be analyzed to monitor the effectiveness of the separation unit and the measurement devices. The step of determining, via the processor, that a measured reading of a parameter of the separations processor is suboptimal may refer to determining via input from a sensor that a parameter, such as temperature of a section of the system performing the process, pressure level at a section of the system performing the process, flow rate at a conduit of the system, pollutant concentration, or some other parameter is at a suboptimal level. Such parameter may be any parameter for which data is stored by the master controller, which may be a computer system. In some embodiments a suboptimal level is determined when the measured reading of the parameter falls out of an acceptable range known by one skilled in the art and the overall output of the separation process is affected negatively. Referring to cleaning of flue gas, optimal conditions may be defined as a ratio of a certain amount of pollutant in the flue gas to a certain amount that is precipitated and removed from the flue gas. Suboptimal conditions may be when the ratio drops to less than 10% of the ratio under optimal conditions; however, depending on the settings of the apparatus, the optimal conditions may be adjusted. For example, in some setting it may be desired to remove 99% of the pollutant by precipitation; in other settings, it may be desired to remove greater than 80% of the pollutant by precipitation. Returning to a substantially optimal range may refer to returning within 5% or greater of the ratio of the optimal conditions; for example, if the optimal ratio is 90%, and the ratio drops to 79%, then that may be considered as a suboptimal condition; then if the ratio returns to between 85% and 100% inclusive, then that may be considered as returning to an optimal condition, which may also mean returning or exceeding an optimal condition threshold.

Processor (700), which may be connected wirelessly or wirelessly to controllers, sensors, and other components of the system, may be any computing processor from a server or master controller adapted for monitoring of equipment.

FIG. 1 is a schematic drawing of a system (101) for testing the effectiveness of a flue gas carbon dioxide separation unit (100). In this example, the separation unit employs cryogenic carbon capture as its separation process. However, other pollutant separation methods may be used. System 101 includes a simulated gas stream (200) composed of nitrogen and carbon dioxide, although other gases may be used. The system also includes supply carbon dioxide (122) and supply nitrogen (120). The supply carbon dioxide (122) and supply nitrogen (120) may be bottled. The supply nitrogen (120) is injected into the system through a valve (114), which may be a solenoid valve, an actuated ball valve, or a mass flow controller. FIG. 1 shows a solenoid valve (114), although a different valve may be used. The supply carbon dioxide (122) is injected into the system through a first mass flow controller (MFC 1) (106). The simulated flue gas stream (200) passes through a blower (112) which regulates the flow rate of the simulated flue gas stream (200). This is done using data from a flowmeter (116) placed after the blower (112), which monitors the flow rate of the simulated flue gas stream (200). The blower (112) may operate to keep the simulated flue gas stream (200) at a constant flow rate set by the operator. This flow rate may be at least 5 SCFM. The simulated flue gas stream (200) may also pass through a first analyzer (102), which may monitor the concentration of carbon dioxide in the simulated flue gas stream (200) before entering a separation unit (100). In the separation unit (100), the carbon dioxide is removed from the simulated flue gas stream (200) and leaves the separation unit (100) as a purified carbon dioxide stream (202). All remaining gas leaves the separation unit (100) as a clean gas stream (204), consisting of nitrogen and any carbon dioxide that was not removed.

The clean gas stream (204) passes through a second analyzer (104), which may also monitor the carbon dioxide concentration. When comparing the carbon dioxide concentration in the clean gas stream (204), as measured by the second analyzer (104), to the carbon dioxide concentration in the simulated flue gas stream (200), as measured by the first analyzer (102), the effectiveness of the separation unit (100) may be monitored. The difference in amount of carbon dioxide between the two streams is equal to the amount of carbon dioxide removed from the flue gas stream. After passing through the second analyzer (104), the clean gas stream (204) is then recycled with the purified carbon dioxide stream (202).

In some preferred embodiments, before recombining with the clean gas stream (204), the purified carbon dioxide stream (202) may pass through a second mass flow controller (MFC 2) (108). In some embodiments, MFC 2 (108) may be replaced by a flowmeter. MFC 2 (108) monitors the flow rate of the purified carbon dioxide stream (202). A PID controller may use data from MFC 2 (108) to enable feed-forward control over MFC 1 (106), meaning data from MFC 2 (108) is fed forward to the PID to control the output of MFC 1 (106), rather than using data from the first analyzer (102). If the flow rate through MFC 2 (108) increases, the flow rate through MFC 1 (106) decreases accordingly to maintain a set constant concentration as monitored by the first analyzer (102). If a process upset occurs and more carbon dioxide is released into the system than is necessary to maintain the set concentration, the flow rate through MFC 2 (108) will be high enough that the PID will output a negative value for the flow rate through MFC 1 (106). In this case, there is excess carbon dioxide in the system that may need to be released through a third mass flow controller (MFC 3 (110)). If the output for MFC 1 (106) is negative, the PID controller will use the absolute value of the negative output as the output for MFC 3 (110). There may be no supply carbon dioxide (122) flowing through MFC 1 (106), and excess carbon dioxide being released from the purified carbon dioxide stream (202) through MFC 3 (110). The following table gives an example of the feed-forward control mechanism.

TABLE 1 CO2 required to CO₂ through maintain setpoint MFC 2 concentration PID Controller MFC 1 MFC 3 (kg/hr) (kg/hr) output (kg/hr) (kg/hr) 0 5 100% 5 0 3 5  40% 2 0 5 5  0% 0 0 7 5 −40% 0 2

In some other embodiments, the PID controller may use data from the first analyzer (102) to control the output through MFC 1 (106) and MFC 3 (110), keeping the concentration of carbon dioxide constant at the set point as monitored by the first analyzer (102). This may render MFC 2 (108) unnecessary. However, MFC 2 may still be used to enable the mass balance described below.

When excess carbon dioxide may be released through MFC 3 (110), the released gas may be vented to the atmosphere, compressed and stored, or returned to the carbon dioxide supply.

When the purified carbon dioxide stream (202) and the clean gas stream (204) combine, the supply carbon dioxide (122) may also be injected via MFC 1 (106). Data from the first analyzer (102) and the second analyzer (104) may be used by the operator or controller, along with data from MFC 1 (106), MFC 2 (108) and MFC 3 (110), to close a mass balance on carbon dioxide around this combination point (107). In some preferred embodiments, an indicator on an HMI may perform the calculations. The mass balance calculation may be used to ensure that all measuring instruments used in the process are calibrated and operating correctly. The calculation is to verify that the mass of the carbon dioxide entering the combination point (107) is equal to the mass of the carbon dioxide leaving the combination point (107). An example calculation uses the following equation:

${{{FT}\; x_{2}\frac{1\; x_{1}}{1\; x_{2}}} + {M\; F\; C_{1}} + {M\; F\; C_{2}\mspace{14mu} M\; F\; C_{3}}} = 0$

Where FT is equal to the flow rate as measured by the flowmeter (116), x1 is equal to the mass fraction of carbon dioxide in the simulated flue gas stream (200) as measured by the first analyzer (102), x2 is the mass fraction of carbon dioxide in the clean gas stream (204) as measured by the second analyzer (104), MFC1 is the flow rate of the supply carbon dioxide stream (400) through MFC 1 (106), MFC2 is the flow rate of the purified carbon dioxide stream (202) through MFC 2 (108), and MFC3 is the flow rate of the excess carbon dioxide through MFC 3 (110). If the mass balance is incorrect, the HMI may signal an error, and the operator may choose to recalibrate the instruments.

The combination point (107) of the purified carbon dioxide stream (202) and supply carbon dioxide stream (400) with the clean gas stream (204) may be located carefully. The combination point (107) may be sufficiently upstream of the first analyzer (102) that the gases are well mixed before passing through the first analyzer (102), and sufficiently downstream of the second analyzer (104) that the purified carbon dioxide and the injected supply carbon dioxide (122) are not picked up by the second analyzer (104).

The stream leaving the combination point (107) is a mixture of the purified carbon dioxide stream (202), the clean gas stream (204), and the supply carbon dioxide stream (400); and may be referred to as the recycled gas stream (404). In some preferred embodiments, the supply nitrogen (120) may then be injected into the recycled gas stream (404) through the solenoid valve (114). The stream that may leave this injection point is the simulated flue gas stream (200), which may then continue through the process toward the separation unit (100). The pressure transducer (118) may be placed after this injection point, and on the suction side of the blower (112). The PID controller may use data from the pressure transducer (118) to control the output of the solenoid valve (114), and keep the simulated flue gas stream (200) at a constant set pressure. In some preferred embodiments, this pressure may be in the range of 0.1 psig to 2 psig. In some other embodiments, such as using a compressed simulated flue gas stream, this pressure may range from 50 psig to 100 psig. The pressure-regulated simulated flue gas stream (200) may then pass through the blower (112) and recycle through the process.

FIG. 2A is an illustration of the system 101 depicted in FIG. 1. It shows one possible arrangement of the embodiment of the flue gas recycling system in FIG. 1. FIG. 2B further illustrates a section of FIG. 2A, showing more detail of the system just before the first analyzer (102) and just after the separation unit (100). In FIG. 2b , the simulated flue gas stream (200) has already passed through the pressure transducer (118) and thus has a constant pressure. It then passes through the first analyzer (102), the blower (112), and the flowmeter (116) before entering the separation unit (100). The figure also shows the clean gas stream (204) and the purified carbon dioxide stream (202) leaving the separation unit (100).

FIG. 3 is a schematic diagram of a system (301) that is similar to system 101. In system 301, all the components and processes of system 101 may be present. Additionally, system 301 contains a fourth mass flow controller, a pressure regulator.

System 301 may be identical to system 101 from the injection point of the supply nitrogen (120) until the separation unit (100). In system 301, the clean gas stream (204) may emerge from the separation unit (100) and pass through the second analyzer (104), just as in system 101. The clean gas stream (204) may also branch off and pass through a fourth mass flow controller (MFC 4) (300). The PID controller may receive data from the pressure transducer (118) and use this data to control MFC 4 (300). MFC 4 (300) may be closed except for when an error occurs and the pressure is too high. In this case, excess clean gas may be released through MFC 4 (300). This released excess clean gas may be vented to the atmosphere or compressed and stored. Clean gas that is not released through MFC 4 (300) may continue to the combination point (107) where the clean gas stream (204), the purified carbon dioxide stream (202), and the injected supply carbon dioxide stream (400) combine.

In system 301, the purified carbon dioxide stream (202) may emerge from the separation unit (100) at a high pressure. This pressure may be around 150 psig. The pressure of the purified carbon dioxide stream (202) may then need to be reduced before recycling through the process. The purified carbon dioxide stream (202) may pass through a pressure regulator (302), which may lower the pressure to approximately 30-50 psig. The purified carbon dioxide stream (202) may then pass through MFC 2 (108), which may further reduce the pressure to the range of the set pressure maintained by the pressure transducer (118) and the solenoid valve (114). After passing through MFC 2 (108), the purified carbon dioxide stream (202) may then proceed to the combination point (107). If there is excess carbon dioxide, as determined by the same methods as system 101, it also may need to be released through MFC 3 (110). There may be a compressor (not shown in FIG. 3) placed after MFC 3 (110) to compress the released excess carbon dioxide, so that it may be stored.

FIG. 4 is a schematic diagram of a simulated flue gas recycling system (401). In system 401, a carbon dioxide supply stream (400) and a nitrogen supply stream (402) are used to create a simulated flue gas stream (200). The simulated flue gas stream (200) may then flow toward a separation unit (100), where it is separated into a clean gas stream (204) and a purified carbon dioxide stream (202). The clean gas stream (204) and the carbon dioxide stream may later combine and are recycled back toward the separation unit (100). The supply carbon dioxide (122) and the supply nitrogen (120) may be injected into the recycle stream as needed.

FIG. 5 is a schematic diagram of a system (501) similar to system 101, wherein the purified carbon dioxide stream (202) is a liquid. It may be the same as system 101 after the combination point (107) of the recycle streams and before the separation unit (100). In system 501 the clean gas stream (204) may emerge from the separation unit (100) and immediately return to the combination point (107), or first pass through the second analyzer (104) as in system 101. The liquid purified carbon dioxide stream (500), however, may pass through a different process than in system 101. The liquid purified carbon dioxide stream (500) may first pass through MFC 2 (108) to measure its flow rate. This data may be used as in system 101 to control the output of MFC 3 (110), which may release excess carbon dioxide when needed. The excess carbon dioxide stream may still be a liquid (502), and may simply be bottled and stored. The liquid purified carbon dioxide stream (500) that is not released through MFC 3 (110) may the pass through a heater (506), which may vaporize the liquid purified carbon dioxide stream (500). The vaporized purified carbon dioxide stream (510) may then continue to the combination point (107), where the carbon dioxide supply may be injected through MFC 1 (106). There may be a mass flow controller (MFC 5) (508) placed just before the combination point to further aid in monitoring the stream and in verifying the mass balance. The stream leaving this combination point (107) may consist of combined clean gas, vaporized purified carbon dioxide, and supply carbon dioxide (122), and may be the same as the recycled gas stream (404) in system 101.

FIG. 6 depicts a diagram of a method for separating and recycling simulated flue gas. Step 602 is forming the simulated flue gas by combining a quantity of at least two supply gases. For example, the simulated flue gas may be formed by combining nitrogen and carbon dioxide. In this case, the nitrogen would be referred to as the inert gas and the carbon dioxide would be referred to as the pollutant gas.

Step 604 is measuring and controlling initial concentrations and flow rates. This may be done using equipment and methods depicted in FIG. 1 and FIG. 3. The carbon dioxide, or other pollutant gas, concentration in the simulated flue gas stream (200) may be monitored and controlled to stay at a set constant concentration. The pressure and flow rate of the simulated flue gas stream (200) may also be monitored and controlled to stay at a constant set value using valves, pumps, flowmeters, and pressure transducers. This may be an especially important step for applications of the method that are for experimental purposes.

Step 606 is passing the simulated flue gas through a separation unit (100) to separate the pollutant gas from the inert gas. The simulated flue gas stream (200) is the only inlet into the separation unit (100). The two outlet streams from the separation unit (100) are a clean gas stream (204), consisting of the inert gas and any pollutant gas that was not removed by the separation process; and a purified pollutant stream, which contains all the pollutant gas that was removed from the simulated flue gas stream (200) during the separation process. For example, if the simulated flue gas stream (200) consisted of only nitrogen and carbon dioxide, then the purified pollutant stream would consist only of carbon dioxide, and the clean gas stream (204) would consist of mostly nitrogen with a small amount of carbon dioxide.

Step 608 is measuring the concentration of pollutant gas in the clean gas stream (204). This may aid in controlling the concentration of the simulated flue gas stream (200), or in monitoring the effectiveness of the separation unit (100). Step 610 involves measuring the flow rate of the purified pollutant gas stream. This may also aid in controlling the concentration of the simulated flue gas stream (200), and may also be used in a mass balance to check the performance of the measurement instruments, as described in system 101.

Step 612 is combining and recycling the separated streams. Once the clean gas stream (204) and the purified pollutant stream have both been measured, they may again combine to form a recycled gas stream (404). Step 614 is injecting clean gas and pollutant gas into the recycled gas stream (404) as needed to maintain the desired concentrations and flow rates as measured in step 604. Once the clean gas and pollutant gas have been injected into the recycled gas stream (404), the simulated gas stream is again formed and may then continue through the process, starting at step 604. 

1. A method for recycling streams in a separations process, comprising: providing a processor communicatively coupled to a non-transitory storage medium, the non-transitory storage medium comprising data storage, the data storage comprising instructions; determining, via the processor, that a measured reading of a parameter of the separations processor is in a suboptimal range; providing an inlet flue gas stream comprising an inert gas and a pollutant gas; separating, via a separation unit comprising a volume of contact fluid selected from the group consisting of aliphatic hydrocarbons with substituted halogens, aliphatic hydrocarbons without substituted halogens, aromatic hydrocarbons with substituted halogens, aromatic hydrocarbons without substituted halogens, cyclic hydrocarbons with substituted halogens, cyclic hydrocarbons without substituted halogens, and combinations thereof, the inert gas from the pollutant gas in the inlet flue gas stream to form a clean gas stream and a purified pollutant gas stream; removing at least 1% of the volume of contact fluid to form a removed volume of contact liquid; performing at least one unit operation on the removed volume of contact fluid, the at least one unit operation selected from a group consisting of increasing the temperature of the removed volume of the content fluid by at least 2 degrees Celsius, decreasing the temperature of the removed volume of the content fluid by at least 2 degrees Celsius, vaporizing at least 5% of the removed volume of the content fluid, removing at least 1 of an amount of impurities disposed in the removed volume of the content fluid, distilling at least 50% of the removed volume of the content liquid, and combinations thereof; injecting the clean gas stream into the inlet flue gas stream to form a flue gas stream of lower pollutant concentration; performing at least one other operation on the purified pollutant gas stream; and repeating the preceding steps of the method using the flue gas stream, at progressively lower pollutant concentration, as the inlet stream until the processor determines that a measured reading of the parameter has been returned to a substantially optimal range or the processor receives a communication informing the processor that the measured reading of the parameter has been returned to a substantially optimal range, or separation process has improved or the processor receives a notification that the separation unit can return to a full load.
 2. The method as in claim 1, wherein the separation unit uses a cryogenic carbon capture process and condenses the pollutant gas; the contact fluid consists of isopentane.
 3. The method as in claim 2, wherein the separation unit can return to a full pollutant load when its temperature drops below a set operational temperature.
 4. The method as in claim 1, wherein a measured pollutant load value for the process is decreased to a lesser measured pollutant load value by decreasing the load for the process, to correct for the measured reading of the parameter of the separations processor that is in a suboptimal range, the method further comprising the step of increasing the load for the process to substantially normal levels after the processor has received a communication that the measured reading of the parameter of the separations processor that previously was in a suboptimal range has been restored to a measured reading of the parameter substantially falling within an optimal range.
 5. The method as in claim 1, wherein the purified pollutant stream is also recycled and reinjected into the inlet flue gas stream.
 6. The method as in claim 1, additionally comprising: injecting a contact fluid as a vapor into the inlet flue gas stream; separating the contact fluid from the purified pollutant gas stream to form a contact fluid stream; performing other desired unit operations on the contact fluid stream; and reinjecting the contact fluid stream into the inlet flue gas stream.
 7. The method as in claim 6, wherein the contact fluid is injected as a liquid into the separation unit.
 8. The method as in claim 6, wherein the contact fluid is selected from the group consisting of aliphatic fluids, aromatic fluids, cyclic hydrocarbons with substituted halogens, and cyclic hydrocarbons without substituted halogens.
 9. The method as in claim 1, wherein the inert gas is selected from the group consisting of nitrogen, oxygen, water, air, and combinations thereof.
 10. The method as in claim 1, wherein the pollutant gas is selected from the group consisting of carbon dioxide, sulfur oxides, nitrogen oxides, fly ash, mercury, arsenic, other pollutants present in flue gas, and combinations thereof.
 11. An apparatus for recycling streams in a separations process; comprising: an inlet flue gas stream, comprising a quantity of inert gas and a quantity of pollutant gas; a contact fluid injected as a vapor into the inlet flue gas stream; a separation unit configured to separate the inert gas from the pollutant and the contact fluid in the inlet stream to form a clean gas stream, a mixed stream; a second separation unit configured to separate the contact fluid from the pollutant gas in the mixed stream to form a purified pollutant stream and a contact fluid stream; an injection point where the contact fluid stream may be reinjected into the flue gas stream; and an injection point where the clean gas stream may be reinjected into the inlet flue gas stream to form a flue gas stream of lower pollutant concentration.
 12. The apparatus as in claim 11, wherein the contact fluid is injected as a liquid into the separation unit.
 13. The apparatus as in claim 11, wherein the contact fluid is selected from the group consisting of aliphatic fluids, aromatic fluids, cyclic hydrocarbons with substituted halogens, and cyclic hydrocarbons without substituted halogens.
 14. The apparatus as in claim 11, wherein the inert gas is selected from the group consisting of nitrogen, oxygen, water, air, and combinations thereof.
 15. The apparatus as in claim 11, wherein the pollutant gas is selected from the group consisting of carbon dioxide, sulfur oxides, nitrogen oxides, fly ash, mercury, arsenic, other pollutants present in flue gas, and combinations thereof.
 16. The apparatus as in claim 11, wherein the clean gas stream is recycled until the separation unit drops below a set operational temperature.
 17. The apparatus as in claim 11, wherein the purified pollutant stream is also recycled and reinjected into the flue gas stream.
 18. An apparatus for recycling streams in a separations process, comprising: an inlet flue gas stream, comprising a quantity of inert gas and a quantity of pollutant gas; a contact fluid injected as a vapor into the inlet flue gas stream or as a liquid into the separation unit; a separation unit configured to separate the inert gas from the pollutant and the contact fluid in the inlet stream to form a clean gas stream and a mixed stream; a second separation unit configured to separate the contact fluid from the pollutant gas in the mixed stream to form a purified pollutant stream and a contact fluid stream; a number of additional unit operations through which the purified pollutant stream or the contact fluid stream may pass; an injection point where the contact fluid stream may be reinjected into the flue gas stream; and an injection point where the clean gas stream may be reinjected into the inlet flue gas stream to form a flue gas stream of lower pollutant concentration.
 19. The apparatus as in claim 18, wherein the flue gas stream comprises carbon dioxide and nitrogen, and the contact fluid is isopentane.
 20. The apparatus as in claim 19, wherein the flue gas stream is simulated, additionally comprising: bottled nitrogen to be injected into a closed loop system; bottled carbon dioxide to be injected into the closed loop system; a solenoid valve through which the injected bottled nitrogen is regulated; a pressure transducer communicatively coupled to the solenoid valve, configured to control the solenoid valve to maintain a constant set pressure; the pressure transducer placed on the suction side of a blower; a flowmeter placed after the blower; the flowmeter communicatively coupled to the blower to maintain a constant flow rate; a separation unit configured to separate the carbon dioxide from the nitrogen in the closed loop system; an inlet stream of nitrogen and carbon dioxide flowing into the separation unit, a first outlet stream of cleaned nitrogen, and a second outlet stream of purified carbon dioxide emerging from the separation unit; a first analyzer configured to monitor the concentration of carbon dioxide in the inlet stream entering the separation unit; a second analyzer through which the cleaned nitrogen stream passes, the second analyzer configured to measure the concentration of carbon dioxide in the cleaned nitrogen stream; a combination point where the purified carbon dioxide stream and the carbon dioxide supply are injected into the cleaned nitrogen stream; the solenoid valve placed after the combination point; a first mass flow controller communicatively coupled to the first and second analyzers, the first mass flow controller configured to regulate the injection rate of the bottled carbon dioxide; a second mass flow controller configured to monitor the flow rate of the purified carbon dioxide stream and enable feed-forward control over the first mass flow controller; and a third mass flow controller communicatively coupled to the second mass flow controller, configured to release excess carbon dioxide. 